The invention relates to apparatus for examining an object by means of ultrasonic waves.
This invention relates to prior art ultrasonic imaging apparatus which comprises:
(a) a cylindrical carrier which is rotatable on a supporting shaft and is provided with n transducers for the emission and reception of ultrasonic energy, which are regularly distributed along the periphery of the carrier; PA0 (b) a drive motor which is coupled to the shaft; PA0 (d) a transmitter; PA0 (e) a receiver; PA0 (f) connection means for connecting the transmitter and the receiver to the respective transducers in succession; PA0 (g) a first display device for the display of an ultrasonic image in the B-mode which is arranged to display an image of a scanned region of the object, in the form of a sector of a circle, the image consisting of m picture lines which together span a sector of a circle, the direction of each picture line correspondingly displaying the direction in which the transducer connected to the transmitter and the receiver is directed during the formation of the picture line; PA0 (h) a second display device for the display of an ultrasonic image in the M-mode, which is arranged to display, as a succession, images formed by the same selected picture line and relating to a plurality of successive instants in time, the successive images of the selected picture line being arranged parallel to one another with the same interline spacing; PA0 (i) a switching member for the selective connection of the receiver to the first display device and/or to the second display device; PA0 (j) a control device which is arranged to actuate the transmitter each time the carrier reaches one of a plurality of predetermined angular positions and to control the switching member so that it connects the receiver to the second display device in each angular position of the carrier in which a respective one of the transducers is directed in a direction corresponding to the selected picture line, and such apparatus will be referred to herein as apparatus of the kind set forth. PA0 (a) a cylindrical carrier which is rotatable on a supporting shaft and is provided with n transducers for the emission and reception of ultrasonic energy, which are regularly distributed along the periphery of the carrier; PA0 (b) a drive motor which is coupled to the shaft; PA0 (c) an angular direction sensing device for determining the angular position of the carrier; PA0 (d) a transmitter; PA0 (e) a receiver; PA0 (f) connection means for connecting the transmitter and the receiver to the respective transducers in succession; PA0 (g) a first display device for the display of an ultrasonic image in the B-mode which is arranged to display an image of a scanned region of the object in the form of a sector of a circle, the image consisting of m picture lines which together span a sector of a circle, the direction of each picture line correspondingly displaying the direction in which the transducer connected to the transmitter and the receiver is directed during the formation of the picture line; PA0 (h) a second display device for the display of an ultrasonic image in the M-mode which is arranged to display, as a succession, images formed by the same selected picture line and relating to a plurality of successive instants in time, the successive images of the selected picture line being arranged parallel to one another with the same interline spacing; PA0 (i) a switching member for the selective connection of the receiver to the first display device and/or to the second display device; PA0 (j) a control device which is arranged to actuate the transmitter each time the carrier reaches one of a plurality of predetermined angular positions and to control the switching member so that it connects the receiver to the second display device in each angular position of the carrier in which a respective one of the transducers is directed in a direction corresponding to the selected picture line, characterized in that the control device is arranged to actuate the transmitter according to a cycle in which each of the n transducers supplies the data for the formation of a corresponding group of m/n picture lines (i.e. during one revolution of the carrier the transducers taken as a whole would supply the data for the m picture lines), said cycle being interrupted for an interrupt period during which a respective operative transducer occupies a position in which it would otherwise supply data for anyone of the n-1 picture lines which directly follow the selected picture line (k) in the numerical sequence of lines the transmitter being actuated at every instant at which any transducer occupies a position in which it can supply data for the selected picture line (k).
(c) an annular position sensing device for determining the angular position of the carrier;
The first display device in apparatus of this kind displays a two-dimensional image of the object under examination, for example, the heart of a patient. To achieve this, a transducer emits an ultrasonic wave in a given direction and subsequently receives the echo signals produced by acoustic discontinuities at different depths within the object. These echo signals are reproduced as dots on a picture line, the direction of the picture line corresponding to the direction along which the transducer is directed, the location of each dot on the picture line corresponding to the distance between the transducer and the relevant acoustic discontinuity. Shortly thereafter, the carrier will have rotated through a small angle, so that the transducer will then emit in a slightly different direction and, consequently, the next picture line will also have a slightly different direction. The successive picture lines together form an image display in the form of a sector of a circle (B-mode display). Successive images relating to a selected picture line, are formed in the same manner, but are each displayed at a different location, for example, as a series of parallel line images on a strip of paper in a recording apparatus. When given acoustic discontinuities move within the object (for example, cardiac valves), the corresponding dots will each time be situated at a different location on the selected picture line, so that successive images of the selected picture line will give an indication of these displacements (M-mode display).
For an accurate display of the displacements, it is important that the number of successive images of a selected picture line per unit of time, should be comparatively large, for example, more than 100 line images per second. It is not possible to form such a large number of successive images of a selected picture line in one second in known apparatus of the kind set forth. Such prior apparatus comprise, for example, four transducers mounted on the carrier which rotates at a speed of 7.5 revolutions per second. Each transducer is excited by the transmitter m times during each revolution so that an image is formed on the first display device four times per revolution, i.e. at a rate of 30 images per second. Each transducer also supplies the data for the selected picture line once per revolution, so that during each second 30 successive images relating to the selected picture line, are also formed.